The present invention relates to an improved rotary union for use in a central tire pressure management system for automatically maintaining the inflation pressure of the pneumatic tires on moving vehicles such as tractor trailers. Typically, tractor trailers utilize the air compressor on the tractor as a source of pressurized air to activate braking systems. The compressor directs air to the reserve air brake tank on the trailer, which generally corresponds to the range of typical inflation pressures in the tires used on trailers. Air from the reserve air brake tank is first directed to the braking system to maintain the air pressure in the braking system. In conventional tire inflation systems, excess air is directed from the tank through a pressure protection valve to a control box for the tire inflation system. The pressure protection valve only opens to direct the air to the control box when excess air pressure is present, thereby preventing air from being directed to the tire inflation system which is needed for the trailer braking system.
The control box contains a pressure regulator which is set to the cold tire pressure of the particular tires on the trailer so as to supply air to the tires at the desired pressure level in the event of a leak. Air is directed from the control box to the leaking tire through one of the trailer axles, which either carries an air line from the control box, or is sealed and functions as an air conduit. The pressurized air carried by the axles communicates with each pair of trailer tires mounted thereon through a rotary union assembly by which air flow is directed from a stationary air line to the valve stems on the rotating tires. Pressure responsive valves are employed between each rotary union assembly and its associated tires so that upon the occurrence of a leak in one of the tires, the resulting pressure loss will cause one of the valves to open and allow air flow from the rotary union assembly to pass therethrough to the leaking tire.
As tire inflation systems become adopted for broader uses, reliability and ease of maintenance, as well as an ability to manage under inflated as well as over inflated tires have emerged as important demands from the industry, accordingly improvements in apparatus and methods of installing tire inflation systems are needed and it is to these needs the present invention is directed.